Undefined arrays

Question

I've been working on a website when I had a javascript problem I made an empty array and then added the following script.

  while(e<=f){
        array[0]=array[0]+x.charAt(e);
        e++;
        console.log(array[0]);
    }

I get the same value that I want but the word "undefined" with it

Can you update this to a runnable minimal reproducible example which demonstrates the problem? — David
– David, Commented Dec 8, 2022 at 20:43
You have to add more information and example code for it to make sense to anyone — imvain2
– imvain2, Commented Dec 8, 2022 at 20:45

David · Accepted Answer · 2022-12-08 20:45:34Z

3

If array is initially empty, then array[0] is initially undefined. So this operation:

array[0]+x.charAt(e)

will produce "undefined" concatenated with some value.

You can conditionally use an empty string when array[0] is undefined, for example:

(array[0] || '') + x.charAt(e)

answered Dec 8, 2022 at 20:45

David

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Comments

yanai edri · Accepted Answer · 2022-12-08 20:52:39Z

0

If you made the array like that

new Array(100)

then a[1] will return you undefined because this is an array of 'empty' - try to make your array like this

const a = Array.from({length: 100}, (item, index)=> index)

with the map function as the second argument

answered Dec 8, 2022 at 20:52

yanai edri

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